1. Field of the Invention
The present invention relates to a seat belt wearing detection device that detects the wearing of a seat belt provided in a vehicle, and in particular, to a seat belt wearing detection device that determines a wearing state of the seat belt based on a signal transmitted by radio communication.
2. Description of the Related Art
A technique for detecting the wearing state of the seat belt provided in a vehicle and displaying the detection result is known. The wearing state is detected by a buckle switch disposed in a buckle device, and a signal indicating the detection result is transmitted by cable from the seat belt to a control unit of the vehicle so that display control or the like is performed.
In a vehicle in which some seats are detachable, a buckle device is provided in a detachable seat. In this case, it has been difficult to connect a signal line for connection with the control unit of the vehicle or to connect a wiring line for supplying electric power. For this reason, a technique for transmitting a signal by radio communication from the seat belt side when seat belt wearing is detected has been proposed.
In Japanese Unexamined Patent Application Publication No. 2008-238947 (known example 1), as shown in FIG. 10, a configuration (seat belt wearing detection device) 900 for transmitting and receiving the wearing state of the seat belt provided in a vehicle as a radio signal is shown. A first transmitter 920 shown in FIG. 10 is provided on the buckle unit side of the seat belt, a second transmitter 930 shown in FIG. 10 is provided on the take-up unit side of the seat belt, and a receiver 940 and other devices shown in FIG. 10 are provided on the vehicle side.
The first transmitter 920 provided in the buckle unit of the seat belt is configured to include a power generation unit 921, a charging unit 922, a first control unit 923, a sensor 924, and an antenna 925. In addition, the second transmitter 930 provided on the take-up unit side is configured to include a power generation unit 931, a charging unit 932, a second control unit 933, a sensor 934, and an antenna 935.
By a preliminary operation of pulling out the belt prior to wearing and a wearing operation of inserting a tongue unit provided at the distal end of the belt into the buckle unit, electric power is generated in the power generation units 921 and 931. Using the electric power generated by the power generation units 921 and 931, signals are transmitted by radio communication from the first and second transmitters 920 and 930 to the vehicle side. The signal transmitted from the first transmitter 920 or the second transmitter 930 is received by the receiver 940 including an antenna 943 provided on the vehicle side, and the wearing state of the seat belt is determined by a vehicle side control unit 941.
In the known example described above, however, since electric power generated by the preliminary operation of pulling out the belt prior to wearing and the wearing operation of inserting the tongue unit into the buckle unit is used, the amount of electric power that can be generated is small. Therefore, it is not possible to increase the transmission time or the number of times of transmission within the generated electric power. Thus, there has been a problem in that it is difficult to ensure the reliability by transmitting a signal continuously (for example, by retransmitting a signal) when a transmitted signal cannot be correctly received due to the influence of electromagnetic noise or the like.